Vulcanization of rubber



Patented Aug. 3,1943

l1 m o bssusBssj-a W 11 Edward sQnmk QflimmQw assignor "to I onsantojchemical CompanyfSt. Louis; M0,); t a corporation ot tpe laware; 1 ,1

a j ,m Drawinzi anine-# A ril 5 SerialNo. 3284185 t This inventionrelates to the viilcanizationof rubber or similar plasticQ Moreparticularly the 1 present invention relates to angimproved process thevulcani zed rubI- It is ant-object .of inventionto vulcanize ofvulcanizing rubberand to her products obtained thereby.-

" 1 UNITED- IATE A E rubber; by .theiaid of a new class of organicacceleratoi-sorvuloanizingagents; Another object is toprovide a class oforganic sulfides which are direct vulcanizing agents. H Another objectis :to

provide an improved pro .'ssof vulcan'izlrtfg rub bet and more particularlytb provide 1a. process in which prevulcanization is substantiallyeliirninated. A furthepobjectfisto extend the useful 7 fness otaccelerators actijvefat lowftemperature i and toprovide new combinationsot'accelerators [Still further objects are" to provide' rubber'briod anote of improved physical properties and ad vancethe arty l l The'vulcanizing agents or accelerators of l invention comprise morphollnesulfides andmore particularly products possessing the probablestructural formula where higher sulfides are desired by reacting thelates to the" use of morpholine sulfides in the j 1 process a of 1 tvulcanizing rubber lwhateverthe method oI-theirpreparation. I n: The new"and preferred classof rnaterials finds v numerous applications inthecuring and, com

poundingaof rubber. Eor 'examplerthey may be i i i used in place :or theusual vulcanizing agents, It

:is preferred however toemploythem in conjun'cj tionlwlth small,amountsfof sulfur, ui.ge.amounts I =0! sulfur much, lessthari would" benecessary for proper-vulcanizatiomwith sulfurpalonemiNumergousadyantagesattend thereplacement of all or i part offthe sulfurrnormally, employedin aI-rub j 1 her] stockby a-rnorpholinesuhlde; For example the, dangerof prevulcanlzinggthe rubberstockaor 1 scorching? ,during' processingoperations prior :;toactual' vulcanizationds "substantially jeliminated. In this connection many otherwise de- :sirable accelerators arel-imitedw or, excludedt-in commercial practice because of;scorchinglfiifll-f Q culties'. As is shown below mam 1f;these"lowlltemperature accelerator may- -be safely handled inaccordance with, theprinciplesof this inven- 1 tion; 1 Eurthermore thenmor'pholine sulfidespro-e vlde vulcanized rubber products r or: superior H agingcharacteristics; Other "advantages" will in y a g e qpartbeapparentandin=partpointed out in the where zc'is anfintegergg Theseproducts asset VIorthwin 'myxco-pending" application SerialQNo i 319,480f filedFebruaryll'l, 1940, maybe prepared by treating morpholine with azsulfurhalide and specific examplesfollowing-r The choice and amount ofthe 'b'articiiieri@; .pholine sulfide to be used varies widely and ofpounding improvement sought, the physical proper'ties desired inthevulcanizate and the like.

sulfides of methyl and ethyl "substituted; morlphollnegare within thescope oigthis invention.

Prep r t n Q t w1vu caniz na,asen ehq lever constitutes no part 101' thepresent invention 3 and the invention is not limited th r o tbllt 7Where used as direct vulcanizing agentsa mar-i .pholine sulfidecontaining at least twoatoins of sulfur per molecule is preferred, inother words a morpholine disulfidejor polysulfldeej The pre rerrednaterials surprisingly have available at vulcanization temperatures allorthe sulrur conrttained in the molecule as judged by their 0min:

were compounded. comprising properties in comparison with sulfur inamounts equal to their sulfur content. Thus the optimum in a given casemay be approximately calculated from its sulfur content. However thereis generally little or no benefit to be derived from employing amorpholine sulfide in an amount 7 amount of a morpholine sulfide to beemployed' greater than that required to furnish about 1.0

part of sulfur based on the rubber although larger amounts may; beemployed if desired. By way. of example, morpholine disuliide contains27.11% sulfur so that 3.7 parts by Weightbased on the rubber correspondto 1.0 part of sulfur.

Again high amounts may be used if desired. Thus 7.4 parts by weight havebeen used to advantage. However, for most purposes and especially inconjunction with 0.05 or moreparts of sulfur considerably smalleramounts are sufficient.

The desirable curing properties of the. preferred materials may beillustrated by compounding a rubber stockccomprising one of themorpholine'sulfides'and vulcanizingthe stock in the V usual manners Inorder to show' the lack of scorch plasticity data on an uncured rubber 7stock containing as the vulcanizing agent a mor pholine sulfide may becompared with tliat on a V H similar stock in which the saidvulcanizing. agent has been replaced by'sulfur; A convenient'meansj, Iof obtaining plasticity data 'isbyr the use one Williams Plastometerdescribed by Williams, In-

7 .dustrial and Engineering Chemistry vol. 16; 101;, 362 (l924)-seealsoKrall ibld 'VO1. '16,. p;-9-22 (1924). A brief. description of themethod em- I ployedinde'termining the plasticity figures set '{forthbelow followsp cylinders oft'Wo' cubic-centimetersdnvolume iare I cutfrom uncured Erubber compounded stocksyand placed in a c0nsitanttempreheatingfithe test pieces of the uncured stock are placed" in the-Williams plastome'terif'which L"in realityqis"aplastometerpressghaving' amovableupper-weighted plate connected to a gaugegraduated in .rl/ o millimeter so as to :measure -the distance-betweenthe upper and lowerplates of th -press." The plastometer is maintaine'd'in a constanttemperature-oven maintained at 7 v Duringthe plasticitytest thepreheateditest movable plate'restin'g'on itfor' exactlythreeminaiitsgat the end oi which period'the readingcon the-gauge is taken, whichreading is called the alastir'zity 'Jfigur'er -'-Inis plasticityfigureifs 'in ralityfthe height of -the rubber test cylinders in;millimeters after the upper movable plate I e: the presshas rested onit for the period'of j threeminutes designated. The lower figuresindicate a less curing of the stock or. a, less f c hy stock. i i

fnowis' limitati'veof the same, rubber stocks I Paris In Paris by Partsby Smoked sheets ofruboer l 100' ,100 100 p Whiting..- 4 148.8 148.8 7148.8 Zincpxide 64. 5 54. 5 .64. 5 Ozokerite 2.5 2. 5 V 2. 5Ste'aric'aci 0.0 0.6' 0'6 333 Black 7 p H I 0. 8 V 0.8 0:8 PhenylBnaphthylamine 2.4 2.4 2.4 Pip'eridine cyclopentamothylene -1dithiocarbamate. 2. .0

ece-remains'inthe plastometer withjthe upp'er i ri pefature oven 'forthetimes and at the tempe'ra- "time indicatcdi Afterthis initial heating,called 7 Ste s lThe stocks so compounded were vulcanized by 5 heatingfordifferent periods of time at the temperature of pounds steam pressurepersquare inch (266 F.).. The modulus and tensile properties of thecured rubber products are given below.

Table I Modulus of clos ticity in lbs/inf V at elongations Tensile Stock7 Cute ol at break 5" I tilts 111. e

Mine. Permit 7 Percent Percent 490 1,255 1,660 48 30' 485 l, 200 L550490 30 505 w 'l, 320 v l, 750 485 60 465 l, 220 l, 550 470 60 480 V l,320 1, 625 490 60v 535 l, 360 1, 7-10 475 Triese moduius and tensile nu'ressnow the deth'e physical properties oflthe A Plasticity dogtaPrcheatin g V f I ilasticity 'sa e f'rne p I, tea-(ea S ow that serching may be materiany r'edu tias s'ofmaterials. The sto bee amiiybornb tors has at 260 i pan ndergo 's'specific embodiments of theinvention but ibfa fds-airpi sfsiirepersduarelhchfThe physibal'p rtof'tlie age-u rubber-"products are 'ivenbelow. 1

aded Cure Tensile at at elongatidns Stock time in 'bfe'ak'ifi 1 7 mins;e N lbs/in. I 013g" f f sfiartiiei see-eat I embodiments} or thesirable' cures obtained by use of the preferred class of. materials; The2.22 parts of morpholi'ne disulfidein' the C stock contains only 0.6part sulfuryet produces a higher modulus product. t an the A' stoli." Amuch smaller amount as employed the 78' stock is sufficient to substan-1 "many 'iiiial cfed by the use of j the preferred 7 tea-isle aged -in V10:40 pounds .stea

The abovedata show the 1 V V 2,826,735 tion rubber stocks werecompounded comprising i Stock 1 D E 1 F a G a Pamb Patchy Pambv Pambu 11 1 MM, WM wziaht weight Smoked sheets of rubber. 10o 100' 1(1) j 100 ra '00 00 60 Zinc '10 10 10 l0 acidtreated2, 4 trimethyldlhydroq i l iL..... z" I 21 2 Piperldlne clo tw methylene thlocarba- 1 ma 1 1fltmlcadd 1 Morpholine nosulllde. 3.8

i a qn The modulus and tensile properties of the below. 1 The stockswere-vulcanized in theus uala manner by heatlngin a press at thetemperature m pressure per square 1 I able physical we 16145185obtainedgby use of the pr 1 1 stocks 6: cornpounded were vulcanized; in"

The plasticity figures showt vthat pre-vulcanizaqtionvof stockscontaining accelerators; active at low temperatures may be avoided byuse of the preferred class ofmaterials asvulcanizin a ents.

1 amounts of sulfur.

wcuredrubber products containing prior. to vul-r 1L canlzation,morphollne monosulfide are SCtfQIthl eferred 'clas'sof":ma'terialsas-vulcanizing agents. l

V f Asiurther'embodimentsof theinventlon rub- V Lber stocks werecompounded comprising 7 1 1 1 H V 3 I 1 m. bi Parts by weight weight 1'100 40 40 .Y' i '15 1 1 1 4 trlmethyl dlhydny 1 1 I q me 1 1 21Di(benwthiazyl thiol dimethyl urea 1. 1. Dlphenyl guanldine phthalate 0.0. Pamflln 0.

the usual manner by heating for difierent periods of time ina press atthe temperature 013- pound'sjper square inch-K300 Fl). The modu- 'lusand tensile properties products are "given below:

TableIV teem r 1 t c y 1 1 Cum at elongatlons ai mt 1 Stock tlmein 1 1.3

11 mhm s./in elong.

12 590 11,560 3,"21o1 V V 760 1 '12 7 an 1,525 3, 50 665 Plasticity datacpo mdedaregivenbelowg p 1 pmucmiaam Pellet?! 1 1 I 7 i 1 1 1 i 1 1 1 1Stock Plasticity V 1 l t t V figure q; 1 Timeln 'lemp., 1 Preheating t 1CF. 1 Plasticity 1 p 1 t Stock 1 1 'rmmm Tern 1 m 1 1 a mo 11 5251 1f 1. 1 2511 200 E17 .672

1.. ,540 200 J ,467 i i i i 200 J 592 1 30 -auo= ,1) w; 1 er si 1 1 g ai g8 V The plasticitydatashowlthe mark'edretarda- 200 1 F '211- 3tionaofscofch obtainedbyuseof ainorpholine 7 G 1 212 1 polysulfideasthelvixlcanizing agent.

The. preferred class of materials are most ad. vantageously employed inconjunction small Forex ample a stock similar to the H stock 'aboyecontaining 125 parts by weight "of "sulfur shows considerable iset-up orpm-vulcanization; after Iminutes, heating at 1 290? Reducing the sulfurto.1.0.Q5}part by weight andadding 1.0 part by Weight of morpholinedisulflde gav eqai stock which showed' a good .curein Qminutes whenheated in a press at the temperature .of 62 pounds steam pressure persquare inch (309 F.) and at the "same time theplas'tleity figure'of-ythls stock after 660 min- 'utes preheating at 200? was lower thanthat ofthe' stockcontalning 1.25 parts of sulfur after 180; minutesspreheating. -1iln.creasing= the Sill-1' 1 :fur to-0.2 5 part inconjunction with; 1.0 part of i I 1 *r'norph'oline disulfide ,gavee.stockwhich cured in 6 minutes at" the sametemperature without greatlyincreasing the scorch. Theplasticlty figurefor the unvulcanizd stockafter 11 hours 1 preheating at 200; F. was. likewise lower than 1 ter:

that of the sulfur stock mentioned; above at 180 minutes'preheating.1

attending the preferredtuse of the morpholine sulfides rubber stockswerecompounded com H prising i ,Stock l K r 1 65 Pam by Parts by Partcbu i iweight weight weight Smoked sheets of rubber 100 100 l 100 P33 CarbonBlack 40 40 t Zlnx oxide 5 5 1 5 Stearic acld 1 1 1 i 1 Paraflin 0.75,0.75 0.15 1 70 Acetone-p-amino d t 1 satlonproduct 1 2 2 1 ,2 j 1Di(benzothiazyl thiol) dimethyl 1 1 urea ..t 1.05 1.105 -1. 05

Duifihenyl guanidine phthal 1 i V 0; 0. 15 0. 45 S ur 1 1. 1 r 1 -0.'50Morpholine disulflde; l .0

of the cured rubber As further illustrative .offlthefdesirable results"'un'dert'o pounds airprssure 'per' square aged rubber productobtainedfrom: the M stoehthat is frsm'thestock containing molihho linetl-i'suliide in conjunction with a small amount of sulfur; .exhioproperties th ueging the usualmanner byheatingv in a press at thetemperature of 5z pounds steampressure per square inch; "Ihe mociulusand;tensile;p1roper}- :The above data show that the vincorporation ofone of the preferred materials ajs a vulcanizing agent in anamountcontaining about 0.40 part of sulfur while giving'a good cure in 12minutes provides; as might be expected, a rubber stock somewhat weakerthan a similar stock -.containing 1.25 .partsby Weight of -sul furg-However replacing 0.5 part of'sulfur has the surprising result ofproviding a vulcanizate possessing physi V cal propertiesmarkedlysuperior to thoseof the sulfur stock, 'Asthe following tableshows, the scorch ha's'likewise been markedly retarded. v

"A further surprising efffeot foundafter arti iiflal-ly a gthekabovedescriheclstocks .by heating in a comb for h and. 18- houi'sat;

ed higher modulus and tensile id either the 1K L stuck after *As furtherspecific embodiments of the inven- :t-ioi'i rubber stocks werecompounded comprising *Stoek V 7 0 r P Parts by. Parts'by iParts byParts-11y weight .'wez'ght weight weight Smoked sheets ofrubber. 100 100100 100 7 W "'bg 40 4.0 40 40 azincoxide v '5 5 5 5 Stearic acidi l 1 r1 1 Mineral acid tre w2,2,4wtrimethyl. dilly-v V U V V V droquinoline 2I 2 2 2 D 'b nzothiazyl thlol) -uznethylurea 1 05 l 05 1 G5 1.05Diphenyl guanidine The stocks so compounded were vulcanilae'zi in theusual manner by heating in a press." g-temperatwre of 62 pounds steampressu e1 'squar'e'i-nch. The modulus and tensile properties I of thecured rubber products &I 6--g-iV8 n'-bel0Wl The 'plasticitydataashdvfthatthe scorch of vurl it euredgrubber stocksis reducedoriiretardedby' :crepe rubber estates The stocks socofmpeunded werevulcanized in Modulus of elass H ticity in lbs/in. 7

Cum at elongations Tensile Uh; Stock 7 time in at break elon' V 7. m...l is .t inlbsJinfl r.

is 7 Percent 12- 410- 1,240 7 3,36 1 700 The above data show thedesirable physical properties of vulcanizates obtained'from; rubber Vstocks'wherein varying proportions o f sulfur are replaced by one of thepreferred lass of materials; c s. 4 i

replacing-a :portionnf the sulfurnormal-ly used as rvulc'anizing;agentrhytonej of the Epreferred -class of materials. I The morpholinesulfide e rubber stock. comprising 7 pale Zinc oxide :f16,suifur '3,stearic aei'diL-fi 'andzmorpholine flisulfisielfi? parts Joy Weight,'gave'a good cure ,in sixty minutes when vulcanized in a press at thetemperature of thirty pounds ofsteampress'ure'rper square inch. In theninety minute'cure this stockshowedr a higher 'moduius'an'd tensilestrength than a siniiiar stojc'k aoceleratedjwith 1;0 part by weight ofmercaptobenzothiazo1e However, when advantage is' taken ftheir'oelerating properties rnorpholine sulfides are" preferably erfiplos e'd'in corijuhction with an accelerator of a different class.

For example non scorching stocks .pos-

' sessin g-ood modulus and tensile characteristics r as 'weli asidesirabl'e, aging resistance have -..leeen 'aebtainedgby use or":tetram'ethykthiuram -m- ;m0- t sulfide or disulfide 'conjunctidpholineusu-lfi:de-.; {111135 acetaldehyderaniline and. formaldehyde-aniline maybe used With advantage; Particularlywith thiazoleaecelerators. do the-vpreferredmclassflof materials show desirable activating properties.

"Typical examples of thiazole acoelerators comprise me rcaptobenzothiazol'e; mercafpto; vphi-:nyl benzothiazole, mercapto haphthothiazole, di-

nitro phenyl benzothiaz yhsul fide, heriz'fotiiiazyl' thio benzoate,di-benzothiazyl 'ciisulfide :ancl the piperid i ne and cyc'l'ohexylaminjegsaits f mercaptob en zothiazole.

' As specific embodiments t meevent-tenants- Htrating the use ofthiazole accelerators in con- ;iu-nction small amounts of'the preferredsr possess..=appreciable accelerating properties andQmay hef-soflused'in i conj nction with -the usual-:iamounts of sulfur;

class ofm terial rubber stocks were compounded amount. that danger ofprevulcanization. is subit comprising i stantially eliminated in thepresence of a 'di-' 3 Stock 1 V s 'r u v w VXH' Pcrtaliu Pariah Partcbfi'j Partalbv Perish weight weight weight weight weight Smoked sheetsoirubbero -10o 100 V 100 3 100 Zineoxide'. 1o 10- 10 1o '3 1 a a t aStearlc acid o. 5 0. 5 o. 5 o. 5 Momptobenzothiamle... 0.5 0.5Di(benlothiazylthiol)dit v a, v msm lu m as 0.5

Ogglobexylsmino thio nzothialolenr Morpholinedisulfldenn 0.10 0.15 0.100.15

The stocks so compounded were" vulcanized in, the usual manner byheating for different periods of time in a press at the temperature 2The above data show the desirable modulus and tensile propertiesobtainedby use of the preferred class of materials as activators, forthiazole accelerators. Still further improvements ingredients than thoseparticularly set forth. The invention islimited solely by thefollowingclaims. 1

Whatis claimed is: v p

1. The process of vulcanizing rubber which comprises heating rubber inthe presence of: a dimorpholyl sulfide.

are intended tobe cause prevulcanization of the Table VII Modulus ,ofelasticity in lbs/in. a Cure at elougations Tensile at Ult Stock time inbreak in e1 mins. lbs/in .0

' i Per cm! 8 460 1, 980 3,100 790 T- 45 550 2, 480 i 4, 000 800 S. 90625 2,330 3, 730 790 '1. 90 715 2,980 3,800 750 U 45 205 665 2,000 905V- 45 260 975 2,280 860 U 90 440 1,625. 3,100. 830 V. 90 495 2,050 3,250790 W 45 360 1,170 1 2,725 860 X 45 250 i 920 2,400 885 W 90 1,230 4,5004,500 700 x 90 1, 365 4, 580 4, 680 c morpholyl sulfide and anaccelerator. otherthan adimorpholyl sulfide.

5. The process of 'vulcanizing rubber which comprises heatingrubber andsulfur in the presence of a dimorpholyl sulfide and an accelerator otherthan a dimorpholyl sulfide;

6."'Ihe process of vulcanizing rubber which comprises heating rubberin'the presence of a dimorpholyl sulfide in such proportion asconprevulcanization of the rubber in the presence of sulfur.

7. The process of vulcanizing rubber which comprises heating rubber inthe presence of a dimorpholyl sulfide containing at least two atoms ofsulfur per molecule andsulfur in an amount such that danger ofprevulcanization is substantially eliminated and an accelerator tendingto rubber in the presence of sulfur. 8. The process of vulcanizingrubber which comprises heating rubber, an accelerator tending to causeprevulcanization of the rubber in the presence of sulfur and at least0.05 part of sulfur in thepresence of a dimorpholyl sulfide containingat least two atoms of sulfur per result from increasing theamounts'ofmorpholine 1 2; The process of vulcanizing rubber which.comprises heating rubber and sulfur in such amountthat danger ofpre'vulcanization is sub-. stantlallyeliminated in the presence of adimorpholyl sulfide.

l 3. The process of. vulcanizing rubber which comprises heating rubberand sulfur in 'such amount that danger of prevulcanization issubstantially eliminated, in the presence of a dimorpholyl sulfidecontaining at least two atoms of sulfur per molecule.

4. The process of vulcanizing rubber which comprises heating rubber andsulfur in such h 55 be obtained by employing other compounding cule.

'jmolecule in such proportion as contains up to M about one part ofsulfur based on the rubber the amount of sulfur being such that dangerof prevulcanization is substantially eliminated.

9. The process of vulcanizing rubberwhich comprises heating rubber inthe presenceof morpholine disuliide.

dimorpholyl polysulfida 11. The vulcanized rubberproduct obtained byheating rubber in the presence of a dimorpholyl 12. The vulcanizedrubber product obtained by,

heating rubber and sulfur in such amount that l dangerofprevulcanization is substantially eliminated, in the presence of adimorpholylsulfide containing at least two atoms of sulfur per mole- 14.The vulcanizedrubber product obtained by heating rubber and'sulfur insuchamount that danger of prevulcanization is substantially eliminatedinthe presence of a dimorpholyl sulfide and an accelerator other'than adimorpholyl sulfide.

15. The vulcanized rubber product obtained by heating rubber and sulfurin'the presence of a.

'dixnorphelyl sulfide and an accelerator other than a. dimorpholy-lsulfide;

V 16. The vulcanized rubber product obtained by heating rubber inthepresence of a dimorpholyl sulfide in such proportion as contains upto about Y one part of sulfur based on the rubber andan;

, heating rubber an acceleratortending to cause.

accelerator tending to cause prevulcanization'of v v the rubber in thepresence of sulfur. 17. The vulcanized rubber product obtained byheating rubber in the presence of a dimorpholyl sulfide containing atleast two atoms of su1-" fur per molecule and sulfur in an amount'suchthat danger of prevulcanization is substantially prevulcanization of therubber in the presence. of sulfur and at least 0,05;partoi sulfur innthepresence of a dimorpholyl sulfide containing at leastrtwoi atoms ofsulfur per molecule in such proportion as contains upflto about one partof sulfurmh-ased ,onthe rubber-the amount of su1- fur being such thatdanger of prevulcanization substantially eliminated. 1O

19. The rvulcanize d'rubber product obtained y heating rubber in thepresence of morpholine 20. The vulcanizedrubber productobtained'bjrlheating rubber in the presenceof adimorpholylp5 polys'ulfide. V

EDWARD S. BLAKE.

